Multi-break gas blast circuit breaker and operating means therefor



Jan. 26, 1965 A. ALDERMAN ETAL MULTI-BREAK GAS BLAST CI UIT BREAKER AND OPERATING MEANS REFOR 5 Sheets-Sheet 1 Filed May 26, 1960 23 12s FIG.5 umiwqfiiowy A k F\ sm k 3,. Sim, BM) h m Jan. 26, 1965 A. ALDERMAN ETAL 3,157,630

MULTI-BREAK GAS BLAST CIRCUIT BREAKER AND OPERATING MEANS THEREFOR Jan. 26, 1965 MULTI-BREAK ALDERMAN ETAL 3,167,630

GAS BLAST CIRCUIT BREAKER AND OPERATING MEANS THEREFOR Filed May 26. 1960 5 Sheets-$heet 3 3+ (Jaw 1n. m

RM W m HAW/AAA B si-L -wu E A S Jan. 26, 1965 A. ALDERMAN ETAL 3,157,630

MULTI-BREAK GAS BLAST CIRCUIT BREAKER AND OPERATING MEANS THEREFOR Filed May 26. 1960 5 Sheets-Sheet 4 1965 A. ALDERMAN ETAL 3,167,630

MULTI-BREIAK GAS BLAST CIRCUIT BREAKER AND OPERATING MEANS THEREFOR Filed May 26. 1960 5 Sheets-Sheet 5 United States Patent Ofilice MULTl-l-RREAK one hoist" cracorr AND @PERATHB G MEANS THEREFQR Alfred Alderman, Stanislaw Mieczyslaw Goneh, and

Henry liowlinson, all of Statiord, England, assignors to The English Electric Company Limited, London, England, a British company Filed May 26, 19%, Scr. No. 31,881 Gaines application Great Britain .i'une 2, 1%?

a Qlaims. or. zenras This invention relates to electric circuit breakers, and is particularly applicable to circuit breakers having two interrupters electrically connected in series.

It is an object of the invention to provide a new and improved construction of electric circuit breaker of the gas-blast type. i

A preferred construction in accordance with the mvention will now be described with reference to the accompanying drawings, in which:

PEG. 1 shows in side elevation the general arrangement of the circuit breaker;

FIG. 2 shows in axial section the internal arrangements of an interrupter unit forming part of the circuit breaker, with the contacts in their closed positions;

FIG. 3 is a view similar to PEG. 2 but representing the condition of the interrupter towards the end of an opening operation thereof;

FIG. 4 is a view of the control mechanism associated with a pair of interrupters;

FIG. 5 is a cross sectional view of part of the control mechanism; and

H63. 6 and 7 show diagrammatically the linkage by which the control mechanism shown in FIGS. 4 and 5 is linked with the primary actuating mechanism in the circuit breaker base.

HG. 1 of the drawings shows the general arrangement of the circuit breaker. A cylindrical receiver 16 for compressed air carries two hollow vertical insulators 11, each supporting from its top cap 12 a pair of short insulating support arms 13, mounted at an angle to the horizor a1 and also at an angle to the centre-line of the receiver to. Each arm l3 supports an interrupter assembly 14, comprising two air-blast interrupter units mounted in opposition by means of a common centre section 15. The interrupters of each pair are connected electrically in series by the centre-section 1e, and the pairs oi' interrupters are also connected in series. The end terminals 17 of the chain of interrupters form the line terminals of the circuit breaker.

The insulators ii, the support arms 13 and the in terrupter units 15 are all in internal communication with each other and with the air receiver iii, and are all therefore filled with compressed air. Exhaust valves m inted on the centre section 16 of each interrupter pair, controlled (by a mechanism hereinafter to be described) so that they open to permit the flow of a blast 0" air through the interrupters and across their arcing paces during opening operations of the circuit breaker. he interiors of the insulators El and the support arms 13 form wide-bore conduits offering negligible resistance to the flow of compressed air. When an exhaust valve '8 is open, the air blast passes outwardly from the centre section 16 of the interrupter pair to the vicinity of the interrupter contacts, whence it returns, its direction of flow having been reversed, to the centre section and is eX- hausted to the atmosphere through the open valve.

The air receiver 16 is mounted at earth potential, but since the air flow through the interrupters is controlled solely by the exhaust valves 13, and since the interiors of the support insulators 11 and the support arms 13 form wide-bore conduits for the compressed air flow, the

3,l7,53 Patented Jan. 26, 1955 air blast is effective at the interrupter contacts immediately after the initiation of the air blast during a switching operation. The circuit breaker structure can be dynamically balanced with respect to the reaction forces of discharged air.

The immediate actuating mechanism for the inter rupter contacts and for the exhaust valves 18 is housed in the interrupter centre sections 16, and is connected by control rods passing down the support arms 13 and the support insulators 11 to the common control apparatus 19, which is arranged not only for the simultaneous control of all the interrupters of the circuit breaker but also for the simultaneous control of other associated circuit breakers, for example forming the various phases of a three-phase circuit breaker.

The construction of one of the individual interrupter assemblies is shown more clearly in FIGS. 2 and 3. The assembly is built up on the casting that forms the centre section 16 of the interrupter pair, and which also houses or supports the control apparatus for the iuterrupters. The insulators 21' that form the musings of the inte rupters are mounted on either side of the centre section 15 by means of flanges 21; further flanges 22 and 23 provide respectively a mounting means for the assembly at the top of the support arm 13, and the connection with the exhaust valve assembly 18.

The fixed contact assembly 24 of each interrupter is supported on the interrupter end plate 2-5, which also forms one terminal of the interrupter. The fixed contact assembly consists essentially of a generally-tubular main contact 26 solidly bolted to the end cap 25 and formed by a series of longitudinal cuts at its inner end into a series or resilient contact fingers 27, biased inwardiy both by their own resilience and by garter springs 23. Within the tube defined by the contact fingers 27 slides an arcing contact 29, provided with a stem 39 that extends into a cylinder 3?. and terminates in a piston 32. A spring 33 biases the arcing contact towards engagement with the moving contact.

The moving contact assembly 453 comprises a tubular moving contact member 41, having the movable throat contact at one end and supported by means of radial arms 53 on a central stem which also carries the internal arcing probe of the contact assembly. A fixed sleeve 45 surrounds the moving contact member 4-1, and is formed at its end nearer the contacts into a series of longitudinal contact fingers biased inwardly by their own resilience and by garter springs 47 to embrace the moving contact member 4.1.

The stem 4 of the moving contact extends through a bore in a wall of a cylinder 48 formed in the interrupter centre section 16, and carries a piston 49 within the cylinder. The selective admission of compressed air into the cylinder 4-8 through ports St and 51 (FIG. 5) can thus control the movement of the moving contact. Spring biasing is applied to the moving contact through the medium of a torque shaft 52 carrying a lever 53 whose end engages a groove 54 machined in the moving contact stem 44. The torque shaft 52 extends to the outer face of the centre section 16, where it is acted upon by biasing springs.

The compressed air conduit formed by the interrupter support arm 13 divides in the interrupter centre section it? into divergent inlet passages 69 leading into the annular enclosure 63 surrounding the contacts. Similarly the exhaust passages 62., which are in communication with the interior of the moving contact member 43., converge to form a common exhaust passage leading to the exhaust valve 43. When the interrupter is closed, the engaged surfaces of the contacts form valve surfaces closing the air passage through the interrupter to the exhaust valve;

enemas-o but the contacts are by-passed by one or more bleed apertures, not shown in the drawing, so that the entire interrupter is in these conditions filled with compressed air.

The exhaust valve 13 comprises a sleeve valve 79 slidable within the valve casing 71 so as to open or close the annular exhaust passage 72 from the interior of the intenupter. A flow deflector 73 forms a guide for the valve. An annular piston 74 is formed around the periphery of the sleeve valve 79 and slides within a cylinder 75 formed within the valve casing. The upper end of this cylinder communicates with the atmosphere through a port 75a, while the lower end communicates through a connection 76 with a control valve for the exhaust valve. Piston by-pass passages 77 are provided to control the movement of the valve. A spring 78 biases the valve to its closed position, in which it engages with an annular seating 79 recessed below the face of the exhaust passage 72; both sides of the piston 74 normally being exposed to atmospheric pressure in the event of spring failure the valve remains biased to its closed position by compressed air supplied through union 76a acting on the differential area of the valve, this differential area resulting from the upper part of the sleeve valve 76 having a slightly greater diameter than the lower part. The valve is substantially balanced in respect of air pressures within the exhaust passage '72, which do not affect its operation.

The immediate control gear for the interrupter assembly is contained within a housing 90 mounted on the side of the interrupter centre section 16. The arrangement is shown in FIG. 4. The torque shafts 52 connected with the moving contacts of the interrupter project into this housing and carry short arms 9i. Compression springs 92, each mounted on a rod 92a between a collar 93 pivoted about a fixed point 94 and a further collar 95 connected with one of the arms 91, and free to slide on the rod 92a, constitute the moving-contact biasing springs. Movement of the contact between its closed and open positions is reflected in a rotation of the torque shaft 52 through an angle of about 30 degrees on either side of the line joining the shaft to the spring pivot 94. The toggle formed by the arm 91 and the spring 92 is thus carried over centre with each complete movement of the contact, and the contact is biased by the spring 92 towards its open or its closed state according to its position in its travel.

The rotation of the spring axes about their pivot 94 is also utilised to provide a contact follow-up motion for application to the control gear. Arms 96 carried by the pivoted collars 93 are connected by links 7 to a triangular floating lever 98; the remaining angle of this lever is pivoted on a long pivoted support arm 99 so as to move in a substantially vertical direction, and is also connected by means of a further link 1% to a point on a valve actuating lever 161. This lever is arranged for the actuation of three valves H32, 103 and 164 in the manner to be hereinafter described. It is suspended by a pivoted bell-crank lever 105, the free arm of which is linked to the interrupter control rod 106 (shown broken for clarity). This rod is connected to the main circuit breaker control mechanism and is movable between the positions indicated in the drawing; it is biased towards its upper or trip position by a spring 107, so that the rod is normally maintainedin tension.

The control linkage just described thus forms a mechanical control scheme for the actuation of the Various control valves N2, 103, 104 which exercise the direct control of the interrupters. This arrangement ensures the minimum time delay in the operation of the various parts of the interrupter on the initiation of .a circuit breaker operation, and requires only a single control connection between the interrupter pair and the main control cabinet.

The functions of the valves H92, 1635, res are as follows:

The valve liii. controls the exhaust valve l3, and comprises a balanced sleeve valve 112 mounted on the valve stem 3.13 and biased by a spring ll. to its closed position. The valve is mounted directly on an inlet flange formed in the interrupter centre section 2.6 and admitting high pressure air to the annular space surrounding the sleeve valve ill; the valve outlet communicates through the connection 76 with the inlet port of the exhaust valve operating cylinder. The use of a balanced construction for this valve 112 results in an arrangement which, although controlling an air conduit of appreciable crosssection leading to the exhaust valve cylinder 75, with consequent minimum delay in the operation of the exhaust valve, puts a comparatively light load on its actuating mechanism, the employement of a pilot valve for the operation of the control valve 192 being therefore unnecessary.

Valve 193 controls the isolating movement of the arcing contact 29 at the conclusion of an opening operation of the interrupter. In its normal position it admits compressed air through a connection 12% to the interior of the arcing contact cylinder 31, and therefore urges the arcing contact 29 toward its engaged position with the moving contact. When the valve is actuated by de pression of its actuating plunger 121, it closes the highpressure air supply to the cylinder of the arcing contact and exhausts the interior of the cylinder to the atmosphere, permitting the withdrawal of the arcing contact 29, under the influence of the pressure in space 61, acting on the right-hand end of the contact 29, to a retracted position within the main contact 26 to provide an isolating contact gap.

The remaining control valve lit-t is a pilot valve for the actuation of a changeover valve 122, for the moving contact o crating cylinders, housed within the interrupter centre section, as shown in FIG. 5. This valve comprises a stem extending within a transverse bore in the centre section 16 and provided at one end with a piston i231 sliding within a cylinder 124-. A connection 1255 connects the cylinder withthe control valve 1%. Valve members 126 and 127 control the admission of corn pressed air from an inlet port 123 to the contact actuating cylinders 48 of the pair of interrupters through ports 5! and 51, and also control the exhausting of air within the cylinder to tmosphere through exhaust passages 12? and 136. A spring 131 biases the valve 122 to the position shown in the drawing; operation of the control valve 1E4 by pressure on its actuating plunger 132 admits compressed air to the inlet 325 of the control cylinder and moves the entire valve 122 to its other extreme position.

The operation of the interrupter assembly through a sequence comprising an opening operation followed by a closing operation will now be described. The sequence commences with the interrupter contacts in their closed positions, as shown in FIG. 2, the various linkages of the control mechanism being in the positions shown in FIGS. 4 and 5 and the exhaust valve 18 being closed.

Although in general the sequence of operations will be described with reference to a single interrupter, both interrupters of any given pair will normally operate simultaneously.

With the contacts closed, the resilient contact fingers 27 of each fixed contact engage the outer annular face of the movable throat contact 4-2, and there is a slight clearance between the contact fingers 27 and the outer face of the arcing contact 29. The main current path through each interrupter thus does not rely on the butt contact between the throat 42 and the arcing contact 29, which are however pressed together by the arcing contact biasing spring 33. The entire interrupter assembly up to the exhaust valve 18 is filled with compressed air. The moving contacts are biased to their closed positions solely by the action of t re contact biasing springs 92 acting through their torque shafts 52. There is no pressure difference across the contacts or across their actuating pistons 49, and therefore there is no tendency for the contacts to move.

An opening operation of the interrupter is initiated by moving the control rod ice upwards from its close position to its trip position. This action displaces the valve control lever lldil to the left through the medium of the suspending bell-crank 195; the left-hand end of the lever lliil strikes the plunger 113 of the exhaust pilot valve 132 and causes this valve to open. Air under pressure is delivered through connections '76 to the l or face of the exhaust valve control piston 74, overcoming the force of the biasing springs 73 and thus moving the exhaust valve 7d to its open position. The movement of the exhaust valve is buttered towards the end of its stroke by the closure by the piston of the port of the by-pass passage 77.

The exhaust valve 13 now being opened, the passages as leading to it from the interior of the moving contacts ll are exhausted to atmosphere. The bleed passage cornmunicating with the passages from the annular space 61 surrounding the contacts is too small to permit pressure to build up on the outlet side, and the engaged faces of the contacts act as valve surfaces to prevent the flow of air into the hollow moving contact. The etiect of the reduction of pressure within the hollow moving contact 41 is thus to produce on that contact an unbalanced force tending to move it away from the fixed contact 24, this movement being assisted in its initial stage by the biasing coring 33 of the arcing contact 29. The initial movement of the moving contact 41 moves the annular outer contact face of the throat contact 42 out of engagement with the resilient fixed contact fingers 27, which move inwardly to engage the outer surface of the arcing contact .29. Movement of th arcing contact and the throat contact 4-2 continues with the contacts in engagement until the arcng contact 29 reaches the end of its travel.

The initial movement of the moving contact, which is effected against the action of its biasing spring $2, moves the contact actuating piston 49 sufficiently to uncover the inlet port of its cylinder, permitting the flow of higi pressure air into the cylinder through this port. Since the other side of the piston 49 is exhausted to the atmosphere through the port 51, the valve 127 and the exhaust passage 3.29, the pressure ditierence across the piston assists in accelerating the moving contact against the diminishing resistance offered by its biasing spring 5 2. The initial phase of the opening operation ends with the separation or" the engaged faces of the arcing contact 29 and the throat contact This permits the initiation of a blast of air through the interior or" the hollow moving contact the exhaust valve to the atmosphere and also, it the interrupter is opening in live circuit conditions, draws an are between the arcing ring 14% of the throat contact and the annular arcing insert 141 of the arcing contact. The air blast flowing into the throat contact immediately transfers this are to the central arcing area 142 of the arcing contact and to the arcing probe 44a of the moving contact assembly, so that only the initial flash is carried by the two arcing rings 14%, 14-1. It will be observed that the main current-carrying contact surfaces do not have to perform any arcing duty.

The movement of the interrupter moving contacts towards their open circuit positions is reflected in the movement of the links 91 forming part of the biasing toggle arrangement, this movement carrying the toggle over centre at about the instant of contact separation so that to springs now tend to assist the piston 49 in driving the contact rapidly to its fully open position. The contact movement is buttered towards the end of the stroke by means of a protuberant boss 143 formed in the face of the con-tact piston 49, which enters the cylinder ex iaust port 51 and restricts the flow of air through it.

FlG. 3 of the drawings shows the position of the contacts as and the exhaust valve 18 as the moving contact assembly approaches the end of its opening travel.

Thus an opening operation of the interrupters is initiated solely by causing the exhaust valve 18 to open.

The movement of the contacts during the operation is reflected in the rotation of the links 9% secured to the pivoted spring collars 93, tending to draw downwards each of the links 97 secured to them. The resultant downward movement of the floating lever 98 is therefore dependent on the total contact movement of the two interrupter-s; after a displacement indicating that both the interrupter contacts have almost reached their fully open positions, the left-hand end of the control lever ltll clears the plunger 113 of the valve 192 and allows this valve to reset. The compressed air acting on the lower face of the exhaust valve control piston 74 is allowed to escape through a bleed aperture, and the exhaust valve resets to its closed position under the action of its biasing springs 78 and of the air pressure on the differential area of the valve. The blast of air through the interrupters cea es, and both interrupter-s remain fully charged with compressed air. The final movement of the valve control lever 101 depresses the actuating plunger 121 of the isolating contact control valve 1&3, exhausting the interior of the arcing contact cylinder 31 to the atmosphere and allowing the arcing contact 29 to withdraw within the contact fingers 27, under the action of the air pressure within the interrupter, to provide a contact gap adequate for circuit isolation at atmospheric pressure. The opening operation is now completed.

Since the downward displacement of the floating lever 93, and hence that of the left-hand end of the valve control lever lid, is dependent on the total contact movement of the two interrupters, failure of one interrupter to operate simultaneously with the other will re salt in the exhaust valve remaining open, and in the main enance of the air blast through both interrupters, until both interrupters have finished their opening operations.

At the completion of an opening terrupter contacts are held in their the action of the biasing springs 92.

To initiate a closing operation of the interrupter-s the control rod ran is moved downwardly to return it to its close position. The first result of this is that the valve control lever lid is moved bodily to the right by the rotation of bell-crank lever 1%; the left-hand end of the lever llll clears the striker 121 of the isolating control valve 1&3, allowing this valve to reset and allowing the arcing contact 29 to move out beyond the ends of the fixed contact fingers 2.7 under the action of its biasing spring 33 and the air pr ssure in the cylinder 51.

The right-hand of the valve control lever ltll actuates the striker 132 of the pilot valve iii l, which operates to admit air under pressure to the actuating cylinder 124 of the changeover valve 122. By this movement port '59 of the contact actuating cylinder is exhausted to the atmosphere through the exhaust passage 13-8, and the other port 51 of the cylinder is supplied with high-pressure air through the port 128. The pressure unbalance across the piston 49 overcomes the action of the biasing spring 92 and drives the moving contact towards its closed position. The toggle levers 9i pass over-centre in the reverse direction and the springs 92 then bias the contacts towards their closed positions; the movement of the contacts is reflected in the upward movement of the floating lever $8, in correspondence with the pivotal movement of the springs, and consequently the valve control lever 1G1 pivots in a clockwise sense about its point of attachment to the bell-crank lever 1%.

The threat contact 42 engages the arcing contact 2 and carries the latter with it as it continues its movement. As the contacts approach the end of their travel, the throat contact 42 engages the contact fingers 27 with its outer annular face, lifting the contact fingers clear of the arcing contact 29 and providing the main current connection through the interrupter. When the contact movement is almost completed, the right-hand end of the valve control lever 101 clears the striker of pilot operation, the inopen positions by a valve 194; the latter resets and cuts d the compressed air supply to the actuating cylinder of the changeover valve 122, which also resets.

The complete interrupter and associated mechanism is now reset in readiness for a further trip operation.

At any stage during the closing operation, the operation may be reversed and the interrupters returned to their open state simply by moving the control rod 106 to its trip position; this action reverses the setting of the pilot valve 1%, and hence that of the changeover valve 122, reversing the motion of the contacts, and except in the extreme initial stages of the closing operation ac tuates the pilot valve 182 to open the exhaust valve. The remainder of a normal tripping operation follows. The mechanism is thus effectively trip-free.

FIGS. 6 and 7 of the drawings show how the control rods 1% of the two interrupter pairs 14 mounted on an insulator 11 pass down the support arms 13 and in the insulator top cap 12 are connected through a bellcrank lever 159 with a single control rod 151 passing down the support insulator. This single rod is maintained in tension by a spring 152 at its upper end. At the lower end of the insulator, a further control rod 153 connects the linkage with a common operating rod 154 connected with the operating mechanism housed in the control cabinet 19. All the control rods are thus maintained in tension by their loading springs, which also serve to accelerate the rods from their close position to their trip position on the initiation of a tripping operation; (alternatively only the actual interrupter control rods 1% may be tensioned, being connected with the control mechanism by a rotary or other positivelyacting linkage). The mechanism in cabinet 19, which is of the trip-free type, includes a latch by which the operating rods are maintained in the close position against the action of the loading springs; a tripping operation is initiated by releasing this latch and allowing the loading springs to move the rods to the trip positions. The control rods are restored to their close position and a closing operation initiated by a suitable motor, either pneumatically, hydraulically or electrically operated, which latches the rods in the close position against the action of the springs. The common operating rod 154, which is also tensioned by a loading spring 155, may pass from the mechanism cabinet 19 to other circuit breakers associated with that shown in the drawing; thus the units of a three-phase circuit breaker may be operated simultaneously by a common control mechanism.

What we claim as our invention and desire to secure by Letters Patent is:

1. A gas blast electric circuit breaker including at least two pairs of interrupting contacts, the movable contacts of the pairs being arranged for simultaneous actuation but having no positive mechanical connection between them, a common valve for controlling a blast of gas through separate contact enclosures for the pairs of contacts and arranged to open at the beginning of an opening operation of the circuit breaker, and means for allowing the said valve to close only after a predetermined total movement of all the movable contacts of said pairs of contacts towards their open positions said means comprising a lever having two points in its length connected so as to move in correspondence with the respective movement of the movable contacts, and having a third intermediate point connected with closing means for said valve so as to allow the valve to close after a predetermined movement of said third point.

2. A gas-blast electriccircuit-breaker comprising two gas-blast circuit interrupters each having a contact enclosure, a co-operating pair of contacts of each interrupter being housed within the corresponding enclosure, one at least of each pair of contacts being movable, a pair of fixed cylinders, a piston cooperating with each cylinder and connected to one of the movable contacts to move therewith, inlet passages communicating with the contact enclosures of the two interrupters and connected to a common source of compressed gas, exhaust passages communicating with the downstream sides of the movable contacts and with the cylinders, 21 common exhaust valve communicating with the exhaust passages, whereby on opening of the exhaust valve the pressure downstream of the movable contacts, and to which the pistons are subjected, falls, thereby both applying simultaneous contact-opening loads to the movable contacts and also, on opening of the contacts, causing a blast of gas to pass between the contacts of each pair from the contact enclosures to the respective exhaust passages, and spring bias means connected to each of said movable contacts; said means including a toggle mechanism comprising a torque shaft connected with each movable contact, an arm secured to said shaft, a compression spring having an abtument at each end, one said abutment being pivotally mounted and the other co-operating with said arm, and guide means inter-connecting said abutments; the arrangement being such that as the movable contacts move between the open and closed positions the arms and guide means pass through a position in which they are aligned, so that when the contacts are in the closed position the compression springs load the movable contacts toward the closed position, and when the contacts are in the open position the compression springs load the movable contacts toward the open position.

3. A gas-blast electric circuit-breaker having an interrupter assembly including two gas-blast interrupter units, said interrupter assembly comprising a centre section; a pair of oppositely-projecting hollow insulators mounted one on each side of the centre section; a pair of end members mounted on the ends of said insulators remote from the centre section; a first pair of contacts supported on and projecting inwardly from said end members and within said hollow insulators; a pair of fixed sleeves projecting in opposite directions from said centre section; a pair of hollow movable contacts slidably mounted each on a respective fixed sleeve and adapted to cooperate each with a contact of said first pair, when the interrupter units are in the closed position; said fixed sleeves and said hollow insulators defining between them a pair of annular passages; hollow support means whereon the centre section is mounted and defining a source of compressed gas; means in said centre section defining first passage means communicating between said source of compressed gas and said pair of annular passages; an exhaust valve mounted on said centre section; means in said centre section defining second passage means communicating between the interiors of said pair of fixed sleeves and said exhaust valve, whereby when said exhaust valve is open and said interrupter units are in the open-circuit position, gas is caused to flow from said source of compressed gas in order through said first passage means, said pair of annular passages, said hollow contacts, the interiors of said pair of fixed sleeves, said second passage means and said exhaust valve; a pair of cylinders within said centre section; a pair of pistons in said cylinders; a pair of stems interconnecting said pistons and said hollow movable contacts; means for selectively supplying gas under pressure to one side of said pistons in the sense to urge said hollow movable contacts towards the open-circuit poistlon and means for simultaneously exhausting the other side of said pistons, whereby, when gas is thus supplied, the pistons, after movement of said hollow movable contacts from the closed-circuit position has been initiated,'assist in accelerating said hollow movable contacts towards the open-circuit position; means for supplying gas under pressure to said other side of said pistons, in the sense to urge said hollow movable contacts towards the closed-ircuit position; and means for simul- 9 taneously exhausting said one side of said pistons, Whereby, when gas is thus supplied, the pistons drive said hollow movable contacts towards their closed-circuit positions.

4. A gas-blast electric circuit breaker as claimed in claim 3 wherein said interrupter assembly also comprises a torque shaft connected with each movable contact, an arm secured to said shaft, a compression spring having an abutment at each end, one said abutment being pivotally mounted and the other co-operating With said arm, and guide means inter-connecting said abutments, the arrangement being such that as the movable contact moves between the open and closed positions the arm and guide means pass through a position in Which they are aligned, so that when the contacts are in the closed position the compression spring loads the movable contact toward the closed position, and when the contacts are in the open position the compression spring loads the movable contact toward the open position.

References Cited in the file of this patent UNITED STATES PATENTS Thommen Aug. 2, Amer Nov. 23, Schneider May 27, Baker et a1. Jan. 27, Forwald Jan. 5, Beatty et a1. Feb. 26, Beatty Feb. 26, Fergus July 28,

CasWell et a1. Oct. 4, Buron Sept. 4,

FOREIGN PATENTS France Oct. 27, France July 27, Italy Mar. 21,

Germany May 9, 

1. A GAS BLAST ELECTRIC CIRCUIT BREAKER INCLUDING AT LEAST TWO PAIRS OF INTERRUPTING CONTACTS, THE MOVABLE CONTACTS OF THE PAIRS BEING ARRANGED FOR SIMULTANEOUS ACTUATION BUT HAVING NO POSITIVE MECHANICAL CONNECTION BETWEEN THEM, A COMMON VALVE FOR CONTROLLING A BLAST OF GAS THROUGH SEPARATE CONTACT ENCLOSURES FOR THE PAIRS OF CONTACTS AND ARRANGED TO OPEN AT THE BEGINNING OF AN OPENING OPERATION OF THE CIRCUIT BREAKER, AND MEANS FOR ALLOWING THE SAID VALVE TO CLOSE ONLY AFTER A PREDETERMINED TOTAL MOVEMENT OF ALL THE MOVABLE CONTACTS OF SAID PAIRS OF CONTACTS TOWARDS THEIR OPEN POSITIONS SAID MEANS COMPRISING A LEVER HAVING TWO POINTS IN ITS LENGTH CONNECTED SO AS TO MOVE IN CORRESPONDENCE WITH THE RESPECTIVE MOVEMENT OF THE MOVABLE CONTACTS, AND HAVING A THIRD INTERMEDIATE POINT CONNECTED WITH CLOSING MEANS FOR SAID VALVE SO AS TO ALLOW THE VALVE TO CLOSE AFTER A PREDETERMINED MOVEMENT OF SAID THIRD POINT. 